Headbox for a paper machine

ABSTRACT

The invention relates to a headbox for a paper machine, comprising: a plurality of distributor-dampening devices; each distributor-dampening device comprising an upright vessel, said vessel having at its bottom a central inlet for feeding of a pulp suspension, a plurality of sectional flow pipes, each being located at the same height and arranged unitormly around the circumference of the said vessel, further comprising dilution water lines for metering of dilution water into each sectional flow pipe; a forming unit having a slit shaped outlet channel extending at least approximately over the width of the paper machine for dispensing of a flat stream of pulp suspension; the sectional flow pipes of each of the distributors being connected to the outlet channel, each of the said sectional flow pipes at least of approximately have the same length.

The invention relates to the headbox of a paper machine.

DE 40 05 281 C1 discloses a headbox of a paper machine, comprising an upright distributor which comprises an inlet suitable for centrally feeding of a flow of a pulp suspension from below, further comprising radial outlets connected to partial flow pipes, all being disposed at the same height (sectional flow pipes) as well as dilution water pipes for metering of dilution water into each of the sectional flow pipes. The said sectional flow pipes lead to a flow chamber including an outlet nozzle having the width of the paper machine for distributing of the said pulp suspension over the width of the machine. The sectional flow pipes each are of equal length and arranged uniformly side by side over the width of the flow chamber.

DE 43 18 430 C2 discloses a headbox for a paper machine, comprising a central distributor which at the same time acts as a dampening device. The said distributor is connected to a modular forming unit which in the direction of the machine width comprises a plurality of rows of modules. At least one further central distributor may be provided, which feeds the same forming unit. The rows of models of each forming unit have connections for all distributors. Pulp suspensions of different properties are fed to the distributors.

According to the above identified prior art techniques each distributor feeds the forming unit of a paper machine over the full machine width. In case there are several distributors provided, those will be fed separately with pulp suspensions of different properties.

Paper machines have become wider and faster in the past. Machine widths of up to 10 m, and operating speeds of 1600 m/min are quite common. Thereby, it becomes increasingly difficult to arrange the sectional flow pipes of a distributor uniformly side by side over the whole machine width and connecting the same to the forming unit. With increasing machine width more pipes become necessary. Such pipes have to be arranged in the same plane, and have to be of the same length in order to achieve a uniform distribution of the pulp suspension. Also, with increasing machine width the requirements of the tolerances to be maintained will increase. High speeds of paper machines require a pressure in the distributor of up to 5 bar. To summarize, the costs of erection and maintenance during operation will increase.

It is the objective of the invention to provide a headbox for a paper machine which headbox is of modular design and which allows for a decrease of the costs and efforts of the erection and of the operation.

The said objective is achieved by using a plurality of upright (vertically standing) distributor-dampening devices, each of them having an upper dome where a pressure pad is created, a lower inlet for feeding of a flow of pulp suspension centrally from below, further comprising a plurality of radial outlets connected to partial flow pipes (sectional flow pipes), further comprising dilution water pipes for metering of dilution water into each of the sectional flow pipes, further comprising a forming unit with an outlet channel of a width corresponding to the width of the paper machine for distributing of the pulp suspension over the machine width, whereby the distributor-dampening devices are arranged parallel to each other, and the sectional flow pipes of each distributor are connected to the forming unit uniformly and side by side.

According to the invention there is provided a plurality of distributor-dampening devices which preferably are of equal size and shape. Each of the said distributor-dampening devices out of the plurality of devices is much smaller than one single distributor as per the prior art, which brings about a number of unexpected advantages as described below.

The differences between a conventional single distributor arrangement and a plurality of arrangements as per the invention may be seen from the following comparison:

For a specific installation one single distributor is used, having a diameter of 1000 mm and a circumference of 3142 mm. Assuming a distance of 70 mm between two neighboured outlets for the sectional flow pipes leaving the distributor, forty-five outlets may be arranged.

The said single distributor may be replaced by two distributors, each having a diameter of 500 mm, and a circumference of 1570 mm. When maintaining the said distance of 70 mm between two neighboured outlets, twenty-three outlets may be provided. This means that approximately the same number of outlets will be obtained (46 versus 45 with the single distributor). It should be noted, however, that the length of each sectional flow pipe with the two-distributor-installation is less than half of the length of each sectional flow pipe of the single-distributor-installation.

The following advantages will be achieved:

-   -   different from prior art installations, when using a plurality         of distributors (distributor dampening devices), due to the         relatively short length of the sectional flow pipes there will         not occur irregularities such as local clusters of fiber         bundles;     -   lower space requirement;     -   the costs of manufacture will be reduced due to the greater         number of parts of equal shape and size;     -   most important: the pressure losses in the sectional flow pipes         between the outlet of the distributor and the forming unit are         reduced to less than half;     -   due to the lower volume of the two (or more) smaller         distributors there are no dead zones and hence less dewatering         or dissociation of the pulp suspension which would result in a         non-uniform fiber distribution.

The first named advantage is of great importance. The inventor has determined that clusters, bundles and specks occur, once the length of the individual sectional flow pipe exceeds a certain value.

There may be provided three or four distributors rather than only two.

Each distributor has a central inlet at the bottom, same as with prior art distributors, whereby the pulp suspension is fed to the various distributors by means of separate suspension feed pipes. Instead, there might be one single suspension feed pipe branching to the inlets of the various distributors.

Also, when using a plurality of distributors as per the invention, it might be advisable to use one single device which is installed upstreams of the said distributors and which serves as a common pressure generator, receiving a main stream of pulp suspension and delivering a number of pressurized streams of pulp suspension, one to each of the plurality of the distributors.

The various distributors may be connected to each other by a pipeline or by pipelines in order to equalize the liquid level in each of the plurality of distributors, such equalizing pipelines being connected above the outlets of the sectional flow pipes to the dome of the distributors.

Preferably, each two neighboured of the plurality of distributors are connected to each other by an equalizing pipeline. Thereby, each equalizing pipeline may comprise a pressure equalizing vessel.

Headboxes of the above type may be combined with each other, thereby providing the option of producing paper which is composed of multiple layers. Thereby, each layer is formed by its own forming unit, which forming unit might be connected to the plurality of distributors. When producing such multi layer sheets e.g. three distributors may be used for the lower layer and three for the cover layer of the sheet. Of course, also further combinations such as e.g. for distributors for the lower layer and two for the lighter cover layer are possible.

The invention is explained in greater detail by the following description preferring to the attached drawings.

FIG. 1 is a schematic view of a first embodiment of a head box for a paper machine.

FIG. 2 is a schematic view of a second embodiment.

The headbox according to FIG. 1 comprises two distributor-dampening devices which are identical with regard to design and dimensions. Pulp suspension is fed to each of the said distributors from below through a central inlet. As can be seen, there is one common feed pipe 10 which branches at 14 into two branch pipes 12.1, 12.2, leading to the central bottom inlet 26.1, 26.2 of the respective distributor 30.1, 30.2.

Each distributor 30.1, 30.2 is standing upright. Each distributor is of essentially cylindrical shape—with the exception of a lower frustoconical portion—having a vertical access. Each distributor 30.1, 30.2 has a plurality of radial outlets for an equal number of sectional flow pipes 16. The outlets all are located at the same height. The outlets are uniformly distributed over the circumference of the respective distributor. There is a liquid level of pulp suspension above the said outlets. Above the liquid level in the so called dome there is maintained super atmospherical pressure.

The headbox comprises a forming unit 18 extending over the full width of the paper machine. Each distributor delivers a plurality of sectional flows of pulp suspension to the forming unit 18. It should be noted, however, that each distributor only serves when half of the forming unit. More precisely, the left hand distributor 30.1 through its sectional flow pipes 16 delivers pulp suspension to the left half of distributor only, whereas the right hand distributor 30.2 delivers pulp suspension through its sectional flow pipes to the right half of the forming unit.

In case there are three distributors—not shown in the drawings—than each distributor would serve only one third of the width of the forming unit 18.

As may further be seen from FIG. 1, there is provided a liquid level equalizing line 20 connecting the domes of both distributors 30.1, 30.2 with each other. i.e. the entries of the equalizing lines 20 are above the liquid levels of both distributors 30.1, 30.2. Also, the equalizing line 20 comprises a pressure equalizing device 22.

As may be seen from FIG. 2. there are provided four distributor-dampening devices 30.1, 30.2. 30.3, 30.4. Here again, each of the distributors is identical with regard to design and dimensions. Each of the said four distributors serves one quarter of the width of the forming unit 18. Thereby, each distributor is located in the middle of the portion of the forming unit 18 which it serves. The exits of the respective distributor to which the sectional flow pipes 16 are connected, again are located at the same height, and uniformly distributed around the distributor. Also, the entries of the sectional flow pipes of a specific distributor are uniformly distributed over that quarter of the forming unit 18, which is to be served by the said distributor. Neighboured distributors are connected to each other by liquid level equalizing lines 20, each comprising a pressure equalizing vessel 22. More in detail, one of the inner distributors is connected via a liquid level equalizer line 20 to the neighboured outer distributor.

The said four distributors are fed with pulp suspension by a main distributor-dampening device 3, which comprises an upright housing 24, again with a central inlet 26 for the pulp suspension from below. The said housing 24 has four exits 28.1, 28.2, 28.3. 28.4, all located at the same height and uniformly distributed around the circumference of housing 24. Each of the said exits 28 are connected to one of the four above mentioned distributors 30.1, 30.2, 30.3, 30.4 via four partial flow pipes 28.1, 28.2, 28.3, 28.4, which all have the same cross section, and are of equal length or almost of equal length. Housing 24 again has a pressurized dome above the liquid level of housing 24 and hence above the said four exits 28.

The main distributor-dampening device 3 is essentially bigger than the four above mentioned distributors 30.1, 30.2, 30.3, 30.4. 

1. Headbox for a paper machine, comprising: a plurality of distributor-dampening devices; each distributor-dampening device comprising an upright vessel, said vessel having at its bottom a central inlet for feeding of a pulp suspension, a plurality of sectional flow pipes, each being located at the same height and arranged uniformly around the circumference of the said vessel, furthor comprising dilution water lines for metering of dilution water into each sectional flow pipe; a forming unit having a slit shaped outlet channel extending at least approximately over the width of the paper machine for dispensing of a flat stream of pulp suspension; the sectional flow pipes of each of the distributors being connected to the outlet channel, each of the said sectional flow pipes at least of approximately have the same length.
 2. Headbox according to claim 1, characterized in that the width of the outlet channel is divided into a number of portions corresponding to the number of distributors, and that one of each said distributors feeds a sectional flow of pulp suspension to a respective portion.
 3. Headbox according to claim 1, characterized in that the said distributors are identical or approximately identical with regard to design and dimensions.
 4. Headbox according to claim 1, characterized in that pulp suspension is delivered by a main feed pipe which is branching into a number of pipes corresponding to the number of distributors, each branching pipe being connected to one of the said distributors.
 5. Headbox according to claim 1, characterized that there is provided a main distributor-dampening device located upstream of the said distributor-damping devices and being of similar or identical design, but bigger in size than the same.
 6. Headbox according to claim 1, characterized in that the distributors are connected to each other by a liquid level equalizing line connected above the outlets of the sectional flow pipes to the dome.
 7. Headbox according to one of claims 1 to 6 claim 1 characterized that neighboured distributors are connected to each other by liquid level equalizing lines.
 8. Headbox according to claim 7, characterized in that at least one of the said liquid level equalizing line comprises a pressure equalizing vessel.
 9. Combination of a plurality of headboxes according to claim 1 for a paper machine intended for the formation of multi layer sheets, comprising forming units for each layer, each forming unit being connected to the same number or different numbers of distributors.
 10. Headbox according to claim 2, characterized in that the said distributors are identical or approximately identical with regard to design and dimensions.
 11. Headbox according to claim 2, characterized in that pulp suspension is delivered by a main feed pipe which is branching into a number of pipes corresponding to the number of distributors, each branching pipe being connected to one of the said distributors.
 12. Headbox according to claim 3, characterized in that pulp suspension is delivered by a main feed pipe which is branching into a number of pipes corresponding to the number of distributors, each branching pipe being connected to one of the said distributors.
 13. Headbox according to claim 2, characterized that there is provided a main distributor-dampening device located upstream of the said distributor-damping devices and being of similar or identical design, but bigger in size than the same.
 14. Headbox according to claim 3, characterized that there is provided a main distributor-dampening device located upstreams of the said distributor-damping devices and being of similar or identical design, but bigger in size than the same.
 15. Headbox according to claim 4, characterized that there is provided a main distributor-dampening device located upstreams of the said distributor-damping devices and being of similar or identical design, but bigger in size than the same.
 16. Headbox according to claim 2, characterized in that the distributors are connected to each other by a liquid level equalizing line connected above the outlets of the sectional flow pipes to the dome.
 17. Headbox according to claim 3, characterized in that the distributors are connected to each other by a liquid level equalizing line connected above the outlets of the sectional flow pipes to the dome.
 18. Headbox according to claim 4, characterized in that the distributors are connected to each other by a liquid level equalizing line connected above the outlets of the sectional flow pipes to the dome.
 19. Headbox according to claim 5, characterized in that the distributors are connected to each other by a liquid level equalizing line connected above the outlets of the sectional flow pipes to the dome.
 20. Headbox according to claim 2, characterized that neighboured distributors are connected to each other by liquid level equalizing lines. 